This PDF file contains the front matter associated with SPIE Proceedings Volume 11081, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

In the context of electromagnetism and nonlinear optical interactions damping is generally introduced as a phenomenological, viscous term that dissipates energy, proportional to the temporal derivative of the polarization. Here, we follow the radiation reaction method presented in [G. W. Ford and R. F. O'Connell, Phys. Lett. A, 157, 217 (1991)], which applies to non-relativistic electrons of finite size, to introduce an explicit reaction force in the Newtonian equation of motion, and derive a hydrodynamic equation that offers new insight on the influence of damping in generic plasmas, metal-based and/or dielectric structures. In these settings, we find new damping-dependent linear and nonlinear source terms that suggest the damping coefficient is proportional to the local charge density, and nonlocal contributions that stem from the spatial derivative of the magnetic field that under the right conditions could modify both linear and nonlinear responses.

This talk is dedicated to the memory of Professor Joe Haus who was a world leader in Nanophotonics. It presents some of our collaborative work in Nanophotonics and highlights some of the exciting new directions presented at 11 of the “International conference on Nanophotonics “series, founded and chaired by Joe . We collaborated on nonlinear optics, stimulated Mie scattering and light manipulation in photonic structures and nanocomposites. Our work on chirality control in composites plasmonic nanostructures and nonlinearity in a medium with epsilon near zero will be covered. Another concept we explored is interaction of structured light carrying both spin angular momentum and orbital angular momentum, with a chiral medium coupling electric and magnetic dipoles, to induce a giant and wavelength tunable chiro-optic response. We developed rare-earth doped fluoride nanocrystals act as optical nanotransformers for in-situ conversion of light from one spectral range to another by multiphoton processes through real intermediate states. The physics of manipulating excitation dynamics in these optical nanotransformers in core-multiple shell nanostructures will be discussed. We recently introduced new energy transfer routes for broadband light harvesting and increased efficiency of both multiphoton upconversion (IR to Visible) and down conversion (Quantum cutting from UV or Visible to Visible or IR) via multistep-cascaded energy transfer in a core-multishell nanoarchitecture. The applications explored of this photon conversion include IR harvesting of photons for photovoltaics, high contrast bioimaging, light activated drug release and optogenetics for neuronal stimulation. Future perspectives will be presented

We summarize our analyses of optical wave and beam propagation in layered media using the transfer matrix method and the Berreman technique using effective medium theory. Examples include multilayer metallodielectric structures which can exhibit hyperbolic dispersion, multilayer dielectric-phase change materials, multilayers of positive index and negative index materials, and multilayers of linear and nonlinear materials. The Berreman technique is used to derive a transfer function of propagation to model beam propagation in hyperbolic metamaterials.

From optical recording to random access memories, Phase Change Materials (PCM) have already revolutionized a number of applications. The materials currently being explored include several chalcogenides glasses of Ge, Te, Sb, Se and Ag, and oxides such as vanadium dioxide. These materials are being explored for number of exciting potentials in photonics, ranging from optical limiters to spatial light modulators. In this talk, I will review our recent work on Ge2Sb2Te5 and VO2, including novel synthesis methods, doping techniques to modify their optical and electrical transition characteristics, glancing angle deposition of nanostructured Ge2Sb2Te5, device applications and future potentials.

Student Contribution: Magnetically-biased non-reciprocal plasmonic media may support Weyl points in their three-dimensional dispersion under certain conditions (for example if the cyclotron frequency exceed the plasma frequency). The projection of these Weyl points onto the two-dimensional surfaces of the plasmonic medium are connected by topologically-protected Fermi arc surface states. In this paper we show that the Fermi arc-based surface plasmon-polaritons can be engineered for three-dimensional topologically-robust, open wave-guiding and radiation. Specifically, in a nonreciprocal plasmonic block we demonstrate that: (a) The propagating surface modes are highly directional due to the hyperbolic dispersion of the Fermi arcs. (b) The modes appear outside the light-cone dispersion and consequently do not lose energy to radiation during guided-wave propagation. (c) The modes do not typically scatter into the bulk although there is no complete band gap in three dimensions due to the presence of Weyl points. (d) Appropriately designed coatings on the surface of the plasmonic block allow the surface modes to become highly-directive leaky modes with tunable radiation properties. (e) The presence of scattering and absorption losses in the plasma does not destroy the topological robustness of the propagating mode. We show that only very high anisotropic losses may lead to a topological transition. The topological protection, directive light propagation, and controllable coupling to radiation modes make this system an attractive platform for complex wave re-routing in three dimensions.

Photonic topology, which is an extension of its counterpart in electron systems [1], triggers significant interest since it is relatively easier to be realized and the topological edge/interface optic transport immune to back scattering can yield novel optic properties and functionality [2, 3]. Recently, we have designed a topological LC circuit [4]. In the planar circuit, capacitors are put on the sites of honeycomb lattice, which shunt the circuit to a common ground, whereas inductors are put over the links between the sites. We clarify that grouping sites into hexagons and making the inductances on the links inside hexagons larger than those between hexagons, a texture respecting the C6v symmetry, induces a topological state. The nontrivial topology characterized by mirror winding numbers has its roots in the Dirac dispersion formed by the honeycomb structure, and is induced by the inductance texture which opens a photonic band gap accompanied by a band inversion between p-like and d-like photonic modes. We have realized the idea experimentally in microstrips, a typical transmission line, and measured accurately the unidirectional microwave transportation governed by the orbital angular momentum (OAM) hosted in hexagonal unit cells [4]. The present approach provides a novel way to generate optic modes with OAM without breaking time-reversal symmetry and space-inversion symmetry. This work is based on the collaboration with Hong CHEN, Tongji University. XH is supported by KAKENHI (17H02913, JSPS) and CREST (JPMJCR18T4, JST). References: [1] H.-M. Weng, R. Yu, X. Hu, X. Dai and Z. Fang: Adv. Phys. vol. 64, 227 (2015). [2] L.-H. Wu and X. Hu: Phys. Rev. Lett. vol. 114, 223901 (2015). [3] Y.-T. Yang, Y.-F. Xu, T. Xu, H.-X. Wang, J.-H. Jiang, X. Hu and Z.-H. Hang: Phys. Rev. Lett. vol. 120, 217401 (2018) [4] Y. Li, Y. Sun, W.-W. Zhu, Z.-W. Guo, J. Jiang, T. Kariyado, H. Chen and X. Hu: Nat. Commun. vol. 9, 4598 (2018).

One-way waveguides have been discovered as topological edge states in two-dimensional (2D) photonic crystals. Here, we design one-way fiber modes in a 3D magnetic Weyl pho- tonic crystal realizable at microwave frequencies. We first obtain a 3D Chern crystal with a non-zero first Chern number by annihilating the Weyl points through supercell modulation. When the modulation becomes helixes, one-way modes develop along the winding axis, with the number of modes determined by the spatial frequency of the helix. These single- polarization single-mode and multi-mode one-way fibers, having nearly identical group and phase velocities, are topologically-protected by the second Chern number in the 4D para- meter space of the 3D wavevectors plus the winding angle of the helix. This work suggests a unique way to utilize high-dimensional topological physics by topological defects.

Topological systems are inherently robust to disorder and continuous perturbations, resulting in dissipation-free edge transport of electrons in quantum solids, or reflectionless guiding of photons and phonons in classical wave systems characterized by topological invariants. These established examples of topological physics, however, do not exhaust all possible topological phases, and recently a new class of topological metamaterials characterized by bulk polarization has been introduced. In addition to edge conduction, these systems have been shown to host higher-order topological states, such as corner states. Here, we introduce topological bulk polarization in two-dimensional Kagome photonic meta-structures, and observe topological transitions as the design parameters are tuned. We demonstrate that our topological meta-structure hosts both 1D edge and Wannier-type second-order corner states with unique properties. The edge states have the angular momentum that reverses for opposite propagation direction, thus supporting directional excitation. We also observe the second order topological states protected by the generalized chiral symmetry of the meta-structure, which are localized at the corners and are pinned to ‘zero energy’. Interestingly, unlike the corner states protected by the conventional chiral symmetry, the generalized chiral symmetry of our three-atom sublattice enables their spectral overlap with the continuum of bulk states without leakage. Our findings open new directions in photonics for controlling propagation and manipulating electromagnetic waves, including within the radiative continuum.

The ability to control the optical scattering response of a material body is of crucial importance in different scientific areas and practical applications, spanning from light trapping for solar cells, to optical tweezers, near-field optical imaging, advanced meta-lenses, etc. In this talk, we review our recent efforts on engineering the optical scattering response at the extreme using complex material platforms and engineered nanostructures. We focus on three main topics in this exciting area. (a) We review some useful physical bounds on scattering and absorption imposed by causality and passivity, and discuss our recent investigation on broadband invisibility and absorption enhancement, with particular focus on the associated limits and the stability issues in the case of active media; we also elucidate the differences and similarities between invisible objects (cloaked objects and anapolar scatterers) and scatterers supporting nonradiating eigenmodes, or bound states in the continuum. (b) As an example of useful application of scattering suppression, we discuss the design of invisible near-field probes for scanning optical microscopy, realized by engineering their impedance at the nanoscale; we also discuss their experimental demonstration at infrared frequencies. (c) Finally, we demonstrate the potential of novel nonreciprocal and topological media to enable even more extreme scattering effects, for example ultra-low-frequency and shape-independent scattering resonances.

We present the operation of a one-way nonlinear mirror, where the image is formed by the process of difference frequency generation on one and the same side of the metasurface, independently of the object location on the left or right. The imaging principle is based on the generalized law of refraction. Regularly, an image of a source, produced by such a deeply subwavelength layer of a nonlinear material, is expected to form on both sides of the surface with a nearly equal efficiency. This symmetric two-side generation is a consequence of the lack of phase-matching constraints within the subwavelength-thin medium. The use of a nanostructured medium allows for control of the generation directionality via interference of the multipolar partial waves produced by the nonlinear response of nanoelements comprising the metasurface. Such interference can result in suppression of the generated field on one side of the metasurface. The approach proposed here allows for a nonreciprocal directionality where this side, additionally, remains unchanged independently of the source location. The approach does not require asymmetry of the nanoelement geometry. Rather, it relies on the existence of shared pathways inducing electric and magnetic multipolar moments in the nanoelement via a nonlinear interaction These pathways allow controlling the phase of both electric and magnetic, nonlinearly produced, multipolar modes by a single (electric or magnetic) vector of the fundamental field of a given frequency. Reversing the direction of that fundamental field thus results in a simultaneous phase switch of both electric and magnetic, nonlinearly produced, multipolar modes, preserving the generation direction.

The prospect of judiciously utilizing both optical gain and loss has been recently suggested as a means to control the flow of light. This proposition makes use of some newly developed concepts based on non-Hermiticity and parity-time (PT) symmetry-ideas first conceived within quantum field theories. By harnessing such notions, recent works indicate that novel synthetic structures and devices with counter-intuitive properties can be realized, potentially enabling new possibilities in the field of optics and integrated photonics. Non-Hermitian degeneracies, also known as exceptional points (EPs), have also emerged as a new paradigm for engineering the response of optical systems. As opposed to standard degeneracies, at an EP, not only do the eigenvalues coalesce but so do the corresponding eigenstates. At such bifurcations, the relevant eigenvectors collapse on each other and as a result, the dimensionality of the system is abruptly reduced. In this case, when a perturbation of strength ε acts on an Nth-order EP (when N eigenvalues and eigenvectors merge), the resulting eigenvalue (frequency) splitting is now proportional to ε^(1/N). This indicates that the sensitivity of a set-up can be enhanced by several orders of magnitude by exploiting the physics of EPs. Among many different non-conservative photonic configurations, parity-time (PT) symmetric arrangements are of particular interest since they provide an excellent platform to explore the physics of EPs for enhanced sensing applications. In this talk, we will provide an overview of recent developments in this field. The use of other type symmetries in photonics will be also discussed.

Through systematically manipulating the couplings in the photonic lattice, the topological nature emerges associated with edge state dynamics. Here, we demonstrate a robust photonic zero mode sustained by a spatial non-Hermitian phase transition in a parity-time (PT) symmetric lattice despite the same topological order across the entire system and a flexible topological photonic lattice with multiple topologically nontrivial dispersion bands. Heterodyne measurements clearly reveal the ultrafast transport dynamics and energy of the edge states at a femtosecond scale, validating the designed topological features.

This paper describes our work on the realization of a non-hermitian Hamiltonian system in time-delay coupled semiconductor lasers consisting of two identical lasers, operated with a small frequency detuning between them, and bidirectionally coupled to each other through optical injection. The effective Hamiltonian for this system is non-hermitian, and, under some assumptions and conditions, reminiscent of two-site paritytime (PT) symmetric Hamiltonians, a topic that is under intense investigation. The dynamical response of the intensity of the lasers as a function of the detuning between them reveals characteristics of a PT symmetric system, and our emphasis is on the features that arise from the delayed coupling. Experimental measurements are in good agreement with numerical simulation of the nonlinear rate equation model that describes the coupled system.

We are pursuing novel functionalities arising from unique capabilities of integrated nanophotonics. In this invited talk, we will introduce our recent two results. First one is a combination of graphene with ultra-narrow plasmonic waveguides efficiently coupled to Si waveguides. This device enables ultrafast all-optical switching with substantially small energy consumption, thanks to unique optical nonlinearity of graphene and ultrastrong light confinement in plasmonic waveguides integrated with efficient mode converters. Second one is based on a periodic modulation of non-Hermitian optical property, namely, a periodic array of gain and loss nanocavities. We will show that such non-Hermitian array leads to strange optical dispersion and nontrivial topological insulating phase, which are fully reconfigurable by controlling the injection current.

Mirror symmetry or parity is a fundamental symmetry in nature found on scales ranging from celestial bodies to atomic structures. It occurs when there is a mirror plane separating a shape or an object into two halves that are mirror images of each other. In the microscopic world described by quantum mechanics and in other wave phenomena, mirror symmetry warrants that the mathematical function ψ(x) describing the underlying object, such as the probability amplitude of finding an electron in a water molecule or an acoustic mode of a violin, is either symmetric or anti-symmetric about the mirror plane. In other words, the relative phase angle θ between the two halves of ψ(x) is either 0 or π. An intellectual curiosity one may have is whether there exists a “complex mirror symmetry” that would remove this restriction on θ, extending it to the entire 2π range while maintaining the identical probability density or intensity distribution of the two halves given by |ψ(x)|^2. Here we show theoretically that this complex mirror symmetry can be realized and observed in an artificial crystal such as a photonic lattice, through the inclusion of a non-Hermitian interface formed by a double-layer of optical gain and loss materials [1,2]. By utilizing complex mirror symmetry and its recursive applications, we find a straightforward paradigm to construct high-order non-Hermitian degeneracies, which can potentially increase the spontaneous emission rate and sensing sensitivity of photonic devices [3,4] by orders of magnitude. References [1] L. Feng, R. El-Ganainy, L. Ge, Non-Hermitian photonics based on parity-time symmetry. Nat. Photon. 11, 752–762 (2017). [2] R. El-Ganainy, K. G. Makris, M. Khajavikhan, Z. H. Musslimani, S. Rotter, D. N. Christodoulides, Non-Hermitian physics and PT symmetry. Nat. Phys. 14, 11–19 (2018). [3] W. Chen, Ş. K. Özdemir, G. Zhao, J. Wiersig, L. Yang, Exceptional points enhance sensing in an optical microcavity. Nature 548, 192-196 (2017). [4] H. Hodaei, A. U. Hassan, S. Wittek, H. Garcia-Gracia, R. El-Ganainy, D. N. Christodoulides, M. Khajavikhan, Enhanced sensitivity at higher-order exceptional points. Nature 548, 187–191 (2017).

Near-Zero-Index (NZI) media have recently received significant attention for enhanced nonlinear optical processes such as the intensity dependent refractive index (IDRI). For NZI materials in the infrared, this effect is generally described as a result of free-electron effects such as excess carrier and hot-electron generation. Yet, many works model the response through the Kerr effect, a bound-electron polarization process exhibiting an instantaneous response and polarization sensitivity that are not observed in NZI materials. The similar dispersions in absorption for NZI and resonant materials enables the Kerr index to be a reasonable approximation, but its origin limits the predictive ability of the model. For example, the non-degenerate Kerr model predicts a diverging n_2 as the material loss tends towards zero. However, this condition would eliminate the absorption of the pump resulting in a vanishing nonlinear interaction. To aid the description of nonlinearities in NZI media, we have developed carrier kinetic models for the IDRI rooted in free electron effects. From this, our model shows that for low loss films, the quality factor n_2/FWHM in fact increases with additional loss, largely due to an significant increase in n_2 which outpaces the increase in breadth. This suggests the difficult task to reduce the loss in NZI materials may not be necessary for applications where the maximum IDRI or modulation is desired. As a result, the carrier kinetic models can more accurately predict the behavior of materials, e.g. in response to varying loss, as well as optimize pumping conditions and couple multiple excitation schemes.

Due to their chemical stability, the large tunability and the mechanical resistance, metal-oxides and metal-nitrides are quickly gaining a privileged role in the realm of plasmonics and photonics, as alternative to standard noble metals in the IR-visible range. Here, by using first principles approaches, we study the optoelectronic and plasmonic properties of representative samples belonging to these two classes of materials. We first investigate the origin of near-infrared plasmonic activity of several metal-oxides: transparent conducting oxides (TCO), such as Al-ZnO and Ta-TiO2, and phases change materials (PCM), namely VO2. In the former case, we investigate the microscopic effects of metal doping (e.g. Al, Ta) [1] and defects (e.g. vacancies) [2] on the optical and electronic properties of TCOs and how this reflects on the plasmonic response of surface-plasmon polaritons or layered hyperbolic metamaterials, in connection with other dielectric media. In the latter case, we focus on stacked heterostructures resulting from the coexistence of metallic and semiconducting phases of VO2. This joint-phase combination, which has been experimentally realized, gives rise to a natural hyperbolic metamaterial, which supports the propagation of volume-plasmon-polariton TM waves (Figure 1) [3]. In the second part of the presentation, we will discuss the plasmonic properties of refractory metal nitrides (e.g. TiN). We first investigate the plasmon dispersion relations of TiN bulk [4] and we predict the stability of surface-plasmon polaritons at different TiN/dielectric interfaces proposed by recent experiments. Finally, by combining first-principles theoretical calculations and experimental optical and structural characterization techniques, we study the plasmonic properties of ultrathin TiN films (2-10 nm) at an atomistic level for the realization of ultrathin metasurfaces with plasmonic nonlinear properties [5-6]. References: [1] A. Calzolari, et al., ACS Photonics 1, 703 (2014). [2] S. Benedetti, et al., Phys. Chem. Chem. Phys. 19, 29364 (2017). [3] M. Eaton, et al., Opt. Express 26, 5342 (2018). [4] A. Catellani and A. Calzolari, Phys. Rev. B 95, 115145 (2017). [5] D. Shah, et al., ACS Photonics 5, 2816 (2018). [6] A. Catellani and A. Calzolari, Opt. Mater. Exp. (2019), in press.

The optical constants - surface susceptibility and surface conductivity of atomically thin MoS₂ can be extracted from ellipsometric parameters using a surface current model. To improve the accuracy and ensure the reproducibility of the extracted optical constants, eliminating possible effects during the measurements is critical. Here, different substrates with various incidence angles in the ellipsometric measurements have been studied and the elimination of back-reflection from substrates have been investigated. Although the ellipsometric parameters vary with the incidence angles and substrates, excellent reproducibility of the extracted surface susceptibility and surface conductivity have been achieved.

Metamaterial theory provides the ability to engineer a custom designed photonic background, which in combination with topological protection will be robust with respect to fluctuations through the intrinsic non-linearity, fabrication imperfections, and thermal noise. We link our recently established group-theoretical approach for topological Weyl materials with a novel quantum-Maxwell-Bloch simulation platform to design and characterise a topologically protected fully three-dimensional epsilon-and-mu-near-zero (phase-locked) nano-plasmonic background for photons. This opens up unique opportunities to achieve optical coherence of quantum emitters at room temperature and to design new lasing states and strong coupling of photon emitters in innovative environments with topological protection against nanoscale structural material disorder.

In this paper, we elucidate the fundamental difference between the magnetic monopoles appearing in Maxwell’s equations and the Dirac equation. Our work shows that a magnetic monopole appears for both photons and massless fermions in the reciprocal energy-momentum space - even for vacuum. Using a Dirac-Maxwell correspondence, we identify the bosonic and fermionic nature of magnetic monopole charge, which is inherently present in the relativistic theories of both particles. While the results in vacuum are expected, we apply this topological theory to 2D photonic (bosonic) materials, in contrast to conventional electronic (fermionic) materials. The specific 2D photonic materials considered in this paper are gyroelectric which possess antisymmetric components of the conductivity tensor. We exploit the Dirac-Maxwell correspondence to show how dispersive gyroelectric media can support topologically massive particles, which are interpreted as photonic skyrmions. However, the differences in spin between bosons and fermions alter the behavior of these bulk skyrmions as well as their corresponding Chern numbers. We then analyze the unique topological edge states associated with nontrivial spin-1 and spin-½ skyrmions, which exhibit opposing helical quantization. This clearly shows how the integer and half-integer nature of monopoles is ultimately tied to the differing bosonic and fermionic spin symmetries. Our work sheds light on the recently proposed quantum gyroelectric phase of matter [32] which supports unidirectional transverse electro-magnetic (TEM) edge states with open boundary conditions (vanishing fields at the edge) - unlike any known phase of matter till date.

Metamaterials---artificial electromagnetic media that are structured on the subwavelength scale---were initially suggested for the realization of negative index media, and later they became a paradigm for engineering electromagnetic space and controlling propagation of waves. However, applications of metamaterials in optics are limited due to inherent losses in metals employed for the realisation of artificial optical magnetism. Recently, we observe the emergence of a new field of all-dielectric resonant metaoptics aiming at the manipulation of strong optically-induced electric and magnetic Mie-type resonances in dielectric and semiconductor nanostructures with relatively high refractive index [1]. Unique advantages of dielectric resonant nanostructures over their metallic counterparts are low dissipative losses and the enhancement of both electric and magnetic fields that provide competitive alternatives for plasmonic structures including optical nanoantennas, efficient biosensors, passive and active metasurfaces, and functional metadevices [2, 3]. Here, we aim to summarize the most recent advances in all-dielectric Mie-resonant meta-optics including active nanophotonics as well as the recently emerged fields of topological photonics and nonlinear metasurfaces. In addition, we also aim to review the physics of bound states in the continuum and their applications in meta-optics and metasurfaces [4]. First, we discuss strong coupling between the modes of a single subwavelength high-index dielectric resonator and analyse the mode transformation and Fano resonances when resonator’s aspect ratio varies [5]. We demonstrate that strong mode coupling results in resonances with high quality factors, which are related to the physics of bound states in the continuum when the radiative losses are nearly suppressed due to the Friedrich–Wintgen scenario of destructive interference. Our theoretical findings are confirmed by microwave and optical experiments for the scattering of high-index subwavelength resonators with a tunable aspect ratio. The proposed mechanism of the strong mode coupling in single subwavelength high-index resonators accompanied by resonances with high-Q factor helps to extend substantially many functionalities of all-dielectric nanophotonics that opens new horizons for active and passive nanoscale metadevices. Next, we discuss how bound states in the continuum can appear in the physics of metasurfaces. We reveal that metasurfaces created by seemingly different lattices of (dielectric or metallic) meta-atoms with broken in-plane symmetry can support sharp high-Q resonances that originate from the physics of bound states in the continuum [6]. We demonstrate a direct link between the bound states in the continuum and Fano resonances, and discuss a general theory of such metasurfaces, suggesting the way for smart engineering of resonances for many applications in nanophotonics and meta-optics. [1] A. I. Kuznetsov, A. E. Miroshnichenko, M. L. Brongersma, Y.S. Kivshar, and B. Lukayanchuk, Optically resonant dielectric nanostructures, Science 354, aag2472 (2016). [2] S. Kruk and Y. Kivshar, Functional meta-optics and nanophotonics governed by Mie resonances, ACS Photonics 4, 2638 (2017). [3] Y.S. Kivshar, All-dielectric meta-optics and nonlinear nanophotonics, National Science Review 5, 144 (2018). [4] K. Koshelev, A. Bogdanov, and Y. Kivshar, Meta-optics and bound states in the continuum, submitted to Science Bulletin; arXiv: 1810.08698v1 (2018). [5] M.V. Rybin, K.L. Koshelev, Z.F. Sadrieva, K.B. Samusev, A.A. Bogdanov, M.F. Limonov, and Y.S. Kivshar, High-Q supercavity modes in subwavelength dielectric resonators, Phys. Rev. Lett. 119, 243901 (2017). [6] K. Koshelev, S. Lepeshov, M. Liu, A. Bogdanov, and Y.S. Kivshar, Asymmetric metasurfaces and high-Q resonances governed by bound states in the continuum, Phys. Rev. Lett. 121 (2018); arXiv: 1809.00330 (2018).

Metasurfaces allow light manipulation and control, from the point of view of planar optics or polarization control, or non-linear light extraction. Their properties rely on the existence of resonant basic elements which are responsible for strongly confined electromagnetic surface modes. We aim at using these modes in order to enhance light-matter interaction. We consider a metasurface in which quantum system are embedded. We study the hybrid excitation between light and matter by using an effective field theory.

Integration of plasmonic metasurfaces and graphene combines the well-known advantages of both: strong field concentration and spectral selectivity of the former with rapid conductivity control of the latter. In this talk, I will describe the state of the art in graphene-integrated metasurfaces. Specific topic of interest that will be discussed in more detail are (i) rapid polarimetry and polarization shaping, (ii) imprinting of chemical potential onto graphene using electrically gated patterned metasurfaces, (iii) detection of mid-infrared radiation using light absorption in graphene placed inside narrow gaps inside plasmonic metasurfaces, and (iv) imprinting phase and amplitude modulation onto nanosecond laser pulses using graphene modulators.

We numerically design and experimentally test a SERS-active substrate for enhancing the SERS signal of a monolayer of graphene in water. The monolayer is placed on top of an array of silver-covered nanoholes in a polymer and is covered with water. Here we report a large enhancement of up to 200000 in the SERS signal of the graphene monolayer on the patterned plasmonic nanostructure for a 532 nm excitation laser wavelength. Our numerical calculations of both the excitation field and the emission rate enhancements support the experimental results. We also propose a highly compact structure for near total light absorption in a monolayer of graphene in the visible. The structure consists of a grating slab covered with the graphene monolayer. The grating slab is separated from a metallic back reflector by a dielectric spacer. The proposed structure could find applications in the design of efficient nanoscale visible-light photodetectors and modulators.

Metamaterials and recently metasurfaces have been a powerful tool to control and manipulate electromagnetic waves and their interaction with matter. Active control of metamaterials is an expanding new direction, which is promising for the realization of novel active devices, such as optical switches, transducers, modulators, filters, and phase shifters at different wavelengths. The integration of passive metamaterials with a variety of tuning mechanisms has been extensively examined to generate active metamaterials that have novel functionalities. In general, there are two major schemes to implement active plasmonic systems. One is based on the integration of active media, that is, phase-transition materials, graphene and carrier-modulated semiconductors, which can respond to thermal, electrical and optical stimuli. The other is based on geometrical reconfiguration, that is, structural tuning of metamaterials. Although the demonstrated devices provide some degree of tunability, their performances are limited to narrow spectra with a small dynamic range due to the material and fabrication limitations. Therefore, these technologies would greatly benefit from a material that yields large tunability over broad spectra. None of the existing materials provides these challenging requirements. Furthermore, the requirement for electrically controlled tunability places another challenge for practical applications of metamaterials. Integrating metamaterial (a split ring resonator, SRR, in this work) in close proximity to graphene surface yields a new type of hybrid metamaterial whose resonance amplitude can be tuned. Previous attempts to integrate graphene with metamaterials yielded very limited modulation in IR and terahertz frequencies. Here, to tune the electrical resonance of metamaterials, we varied the charge density on graphene layer via ionic gating. It should be emphasized here that the technical challenge for graphene-based microwave devices is the requirement of large-area devices owing to the centimeter scale wavelength. To overcome this challenge, large-area graphene by chemical vapor deposition (CVD) on copper foils is used, which enables the realization of the microwave metamaterials. At 0 V, the device yields a resonance at 11.82 GHz with a resonance transmittance of −60 dB. When we applied a bias voltage, electrons and holes accumulate on the graphene electrodes and yield significant damping that diminishes the resonant behavior. For example, at 1.5 V, the resonance transmittance is -12 dB. Figure 2 shows the voltage dependence of the amplitude of transmittance at resonance and the phase at 11.82 GHz. The phase of the transmitted signal varies from -30° to 70°. These active metamaterials enable efficient control of both amplitude (>50 dB) and phase (>90°) of electromagnetic waves. The operation frequency of these metamaterials can be easily scaled up to the terahertz and higher frequencies. Large modulation depth, simple device architecture, and mechanical flexibility are the key attributes of the graphene-enabled active metamaterials. We anticipate that the presented approach could lead to new applications ranging from electrically switchable cloaking devices to adaptive camouflage systems in microwave and terahertz frequencies.

While plasmons in noble metal nanostructures enable strong light-matter interactions on nanometer length scales, the overabundance of free electrons in these systems inhibits their sensitivity to weak external stimuli. Countering this limitation, doped graphene has recently arisen as an actively-tunable material platform for plasmonics, offering extreme electromagnetic field concentration for the price of significantly fewer electrons [1,2]. Here we investigate transient modulation in the optical response of nanostructured graphene associated with the absorption of individual plasmons. We base our analysis on complementary classical and quantum-mechanical simulations, which reveal that the energy of a single plasmon, absorbed in a small, lightly-doped graphene nanoisland, can sufficiently modify the temperature of its electrons and chemical potential to produce substantial changes in the optical response within sub-picosecond timescales, effectively shifting or damping the original plasmon absorption resonance peak and thereby blockading subsequent excitation of a second plasmon. The thero-optical single-plasmon blockade consist in a viable ultra-low power all-optical switching mechanism for doped graphene nanoislands, while their combination with quantum emitters could yield applications in biological sensing and quantum nano-optics. [1] F. J. García de Abajo, ACS Photon. 1, 135 (2014). [2] J. D. Cox and F. J. García de Abajo, Optica 5, 429 (2018).

The field of plasmonics has been largely focused on utilizing either conventional materials in the form of thin films, interfaces and nanoparticles, or 2D materials. Yet, the material optical properties’ evolution in the transdimensional regime between 3D and 2D has remained underexplored. In such transdimensional materials that have thickness of only a few atomic layers, the material’s optical and electronic properties are expected to show unprecedented tailorability compared to their 3D counterparts and conventional thin films. Transdimensional materials are expected to show extreme sensitivity to external optical and electrical stimuli thus forming an attractive platform for dynamically tunable nanophotonics.

Two-dimensional (2D) transition-metal dichalcogenides (TMDCs) are an excellent candidate for realization of a large range of optoelectronic devices on a wide variety of substrates. In this talk, a new approach based on alloying is presented for the formation of lateral heterostructures in 2D TMDCs with unprecedented control over the in-plane device profile and operation wavelength. This approach can be used for post-growth tuning of the optoelectronic properties of the planar structures as well as fabrication of optoelectronic devices such as planar diodes, light emitters, and photodetectors with exotic characteristics. Details of the material formation and properties as well as device fabrication and characterization in such 2D structures will be presented and discussed. In addition, the potential of this platform for the formation of advanced quantum nanostructures structures such as quantum dots and quantum wires will be discussed.

Hexagonal boron nitride (h-BN) crystals possess ultrawide electronic bandgap of 5.9 eV and excellent chemical and thermal stability. Nanometer-scale thin films and atomic layers derived from the layered bulk of h-BN crystals have been widely adopted for enabling new two-dimensional (2D) devices and systems, thanks to its excellent dielectric, optical, mechanical, and thermal properties. Lately, h-BN thin layers have also emerged as an attractive material and device platform for nanoscale optics, photonics, and quantum engineering. In this proceedings paper, we report on some of our studies and initial results toward developing integrated photonic circuitry based on this van der Waals (vdW) layered crystal. The first part summarizes our effort on the creation and optical characterization of defect-related quantum emission in exfoliated and dry-transferred h-BN flakes. Based on the statistics from our measurements and state-of-the-art knowledge in the field, we have identified a group of emitters with emission wavelength around 710 nm exhibiting large Debye-Waller (DW) factor. We then describe optical waveguide and cavity designs at the wavelength range of interest, with the aim of achieving high optical cooperativity. Combined with our studies in ultrathin h-BN crystalline nanomechanical resonators and phononic waveguides, these new explorations in quantum emitters will help pave the way to facilitating h-BN photonic devices and integrated systems for both classical and quantum applications.

Optical antennas made out of van der Waals material with naturally occurring hyperbolic dispersion is a promising alternative to plasmonic and high-refractive-index dielectric structures in the practical realization of nanoscale photonic elements and optical components. Here we show that antenna made out of hexagonal boron nitride (hBN) possesses different resonances enabled by the supporting high-k modes and their reflection from the antenna boundaries. Multipole resonances cause the decrease in the reflection from antenna array to zero, which can be ascribed to resonant Kerker effect satisfying generalized zero back-scattering condition for particles in the array. Reflection and transmission through the van der Waals heterostructure with hBN antennas array can be tailored and actively switched by tuning optical properties of two-dimensional materials. Transdimensional photonic lattices consisting of resonant hBN antennas in the engineered periodic arrays have great potential to serve as functional elements in ultra-thin optical components and photonic devices.

Within the last two decades, it has been theoretically shown and experimentally measured that the radiative heat transfer between bodies in the near-field significantly exceeds the blackbody limit. This enhancement in heat transfer arises from evanescent surface waves, for example surface plasmon and surface phonon polaritons, that can tunnel between bodies at different temperatures. This result holds promise for applications in nano-imaging and lithography, thermophotovoltaics, nanoscale refrigeration and thermal circuitry. Although significant progress has been made in near-field heat transfer using passive materials, such as plasmonic metals and polar dielectrics, realizing actively tunable near-field heat transfer modules is of fundamental importance for controlling the photon heat flux. In this talk, analogously to its electronic counterpart, the metal-oxide-semiconductor (MOS) capacitor, we propose a thermal switching mechanism based on accumulation and depletion of charge carriers in an ultra-thin plasmonic film, via application of external bias. In our proposed configuration, the plasmonic film is placed on top of a polaritonic dielectric material that provides a surface phonon polariton thermal channel, while also ensuring electrical insulation for application of large electric fields. The variation of carrier density in the plasmonic film enables the control of the surface plasmon polariton thermal channel. We show that the interaction of the surface plasmonic mode with the surface phonon polariton significantly enhances the net heat transfer. We study SiC as the oxide and explore three classes of gate-tunable plasmonic materials: transparent conductive oxides, doped semiconductors, and graphene, and theoretically predict contrast ratios as high as 225%.

Unlike conventional optical components, which often present physical obstructions to the miniaturization of optoelectronic devices, the control of light using flat optics has attracted much recent attention due to unique technological opportunities presented by these devices. Optical metasurfaces, which are composed of rationally designed nanostructures, are proposed to replace some of the conventional optical elements given their compact size and more importantly, the ability to produce spatially varying phase change, amplitude modulation and polarization conversion of incident light over subwavelength dimensions. For example, a compact, flat lens with dynamically tunable focal length will be an essential component in advanced reconfigurable optical systems. Although there have been some successful demonstrations of active metalenses recently, they all work in the transmission configuration. Here, we design and realize the first reflection type, tunable lens (i.e., metamirror) operating in the visible regime (670 nm). With a designed hyperboloidal phase profile, the metamirror is fabricated on a substrate driven by external force, so its focal length can be adjusted dynamically. It is shown that the focal length can be continuously adjusted by up to 45% with a 0 to 20% lateral stretching of the substrate, while maintaining diffraction-limited focusing and high focusing efficiency. Our design as a flat optics element has strong potential in widespread applications such as wearable mixed reality electronics, biomedical instruments and integrated optics devices.

Fast propagation speed and low decoherence rates arguably make photons the only realistic candidates for realizing quantum networks [1]. The operation bandwidth of the devices required for photonic quantum information processing is limited because of photons’ relatively weak interaction with matter. As a result, the bitrate of most of today’s photonic quantum networks is limited to the kHz range. Enhancing light-matter interaction is possible using dielectric resonators but the speed of the resulting devices will be eventually limited by the high quality factors. Plasmonic materials used along with the conventional dielectric photonic circuitry allow to dramatically enhance light-matter interaction with significantly weaker constraints on both the operating wavelength range and the achievable bitrate [2]. We will present our current and planned studies in the context of developing a plasmonic-dielectric platform for integrated quantum networks. We will focus on two recent realizations of high-speed photonic components: the brightest room-temperature single-photon source based on an NV center in nanodiamond coupled to a nano-patch antenna [3] and a 100 GHz integrated plasmonic modulator with insertion loss comparable to that of dielectric components [4]. Building quantum photonic devices with nanoscale footprint and operating speeds exceeding kT/h promises the realization of scalable THz-speed room-temperature quantum networks. In addition, we present our new results on the efficient analysis of quantum optical measurements using machine learning-based techniques. References [1] J. L. O’Brien, A. Furusawa, and J. Vučković, “Photonic quantum technologies,” Nat. Photonics, vol. 3, no. 12, pp. 687–695, Dec. 2009. [2] S. I. Bozhevolnyi and J. Khurgin, “Fundamental limitations in spontaneous emission rate of single-photon sources,” Optica, vol. 3, no. 12, 2016. [3] S. I. Bogdanov et al., “Ultrabright Room-Temperature Sub-Nanosecond Emission from Single Nitrogen-Vacancy Centers Coupled to Nanopatch Antennas,” Nano Lett., vol. 18, no. 8, pp. 4837–4844, Aug. 2018. [4] C. Haffner et al., “Low-loss plasmon-assisted electro-optic modulator,” Nature, vol. 556, no. 7702, pp. 483–486, Apr. 2018.

All-dielectric metasurfaces are a versatile platform to investigate a host of exotic electromagnetic responses. Effects including high absorption, bound-states-in-the-continuum (BIC), and Huygens’ surfaces have been shown. However, conventional dielectric metasurfaces achieve their properties through geometry alone, and are consequently static. The usefulness for realistic applications is thus inherently limited. In order to overcome the limitations of static all-dielectric metasurfaces, we utilize optical photodoping to attain precise and ultrafast control. We demonstrate the optical control of Huygens’ metasurface (HMS) absorbers, and a dynamic BIC at terahertz frequencies. The BIC realizes a high-quality factor resonance Q ~ 8700 which may be modified by over 2 orders of magnitude by photodoping with bandgap light. The HMS absorber achieves an intensity transmission modulation depth of 99.93% and an associated phase change of greater than π/2 rad. Coupled mode theory and S-parameter simulations are used to elucidate the mechanism underlying the dynamics of the metasurfaces. Similar to metal-based metamaterials, both systems may be scaled in size to operate in nearly any band of the electromagnetic spectrum. The dynamic photonic systems studied here show wide tunability and versatility which are not limited to the spectral range demonstrated, offering a new path for reconfigurable metasurface applications. Our demonstration of dynamic control can be leveraged for applications requiring ultrafast response, or spatial filtering, leading to more compact, efficient, and versatile photonic components.

I review our recent findings on lasing / condensation in plasmonic nanoparticle lattices^1-5. The system properties can be tailored with high precision, including the lasing / condensation energies, linewidths, as well as the dimensionality of the feedback. For a 2-dimensional (2-D) square lattice, we identify lasing in the bright and the dark mode of the system¹. By reducing the dimensionality to 1-D we observe the dark mode lasing2. In broken symmetry 2-dimensional rectangular lattices, we observe multimode lasing³. In honeycomb lattices with hexagonal symmetry, we observe 6 beams with specific off-normal angles and polarization properties corresponding to six-fold symmetry of such a lattice⁴. Finally, I review our recent studies in plasmonic Bose-Einstein condensation in plasmonic lattices⁵.

Plasmonic color filtering and color printing have attracted considerable attention in recent years due to their supreme performance in display and imaging technologies. Although various color-related devices are designed, so far very few studies have touched the topic of dynamic color generation. In this article, dynamic color generation is demonstrated by integrating plasmonic nanostructures with vanadium dioxide based on its tunable optical properties through insulator–metal transition. Periodic arrays of silver nanodisks on a vanadium dioxide film are fabricated to realize different colors, relying on the excitation of localized and propagating surface plasmons, and Wood’s anomaly. By tuning spatial periodicity of the arrays and diameter of the silver nanodisks, various colors can be achieved across the entire visible spectrum. Further, using insulator–metal transition of vanadium dioxide, the colors can be actively tuned by varying temperature. The approach of dynamic color generation based on the phase transition of vanadium dioxide can easily realize diverse color patterns, which makes it beneficial for display and imaging technology.

In the six decades since F. J. Morin’s seminal paper describing the insulator-to-metal transition (IMT) in vanadium dioxide (VO2) appeared, it has been cited more than three thousand times and touched off a search for electronic applications – such as the Mott transistor – that continues up to the present. Photonic applications are now also emerging as studies of ultrafast dynamics in the photo-induced phase transition (PIPT) have yielded an increasingly nuanced, microscopic understanding of the dynamics of the IMT in thin films and nanoparticles of VO2. It appears that VO2 can function as a virtually universal phase-changing oxide, especially for those photonic applications requiring low energy and high switching efficiency. Moreover, the large changes in the VO2 dielectric function can be leveraged to control plasmonic and phononic responses through the use of resonant and other field-enhancing structures. This introduces a critical element of reconfigurability on time scales ranging upwards from the sub-picosecond domain across a broad variety of hybrid structures. After highlighting key elements of the ultrafast dynamics triggered by the PIPT, I will review recent and unpublished applications of the PIPT in the near and mid-infrared to (1) switching in silicon photonics, (2) controlling hyperbolic phonon polaritons in hexagonal boron nitride, (3) constructing plasmonic memory and color arrays, and (4) designing reconfigurable arrays for imaging and sensing. For many applications, the optical losses require that one use as little VO2 as possible, highlighting the critical importance of future materials engineering as well as PIPT studies in nanostructures of sub-micrometer dimensions.

We discuss some of our recent efforts in designing nanophotonic structures for the purpose of analog optical computing. Examples include image processing, and training of optical neurotrophic networks.

We present our latest results on silicon photonics neuromorphic information processing based a.o. on techniques like reservoir computing. First, we dicuss how passive reservoir computing can be used to perform non-linear signal equalisation in telecom links. Then, we introduce a training method that can deal with limited weight resolution for a hardware implementation of a photonic readout.

Leveraging topological protection in the photonic domain could lead to new ways to transport information on-chip, potentially increasing its robustness to scattering at disorder. We realize a photonic analogue of topological insulators based on the quantum spin Hall effect in symmetry-broken photonic crystals. We directly observe the propagation of topological edge states at telecom wavelengths in a silicon-on-insulator platform. Analyzing their properties through their far-field radiation allows characterizing their inherent spin, dispersion, and propagation. We reveal that the radiation of the topological states carries a signature of their origin in photonic spin-orbit coupling, linking the unidirectional propagation of two states with opposite pseudospin to circular far-field polarization. Polarimetric Fourier spectroscopy allows mapping the edge state dispersion and characterize their quality factors. The positive and negative group velocity modes can be selectively excited with circular polarization of opposite handedness. Moreover, we detect a small gap at the edge state crossing that is related to spin-spin scattering, inherent to the symmetry breaking at the edge, and a defining difference between photonic and electronic topological insulators. We image edge state propagation in real-space microscopy, and show how they can be routed at sharp waveguide junctions, attesting to their topologically protected nature. Thus, we observe the unique nature of topologically protected light transport in photonic crystals, through a technique that holds great promise for developing novel topological systems for various applications, including integrated photonic components, quantum optical interfaces, and nanoscale lasing.

Photonic neural networks (PNN) are a promising alternative to electronic GPUs to perform machine-learning tasks. The PNNs value proposition originates from i) near-zero energy consumption for vector matrix multiplication once trained, ii) 10-100 ps short interconnect delays, iii) weak required optical nonlinearity to be provided via fJ/bit efficient emerging electrooptic devices. Furthermore, photonic integrated circuits (PIC) offer high data bandwidth at low latency, with competitive footprints and synergies to microelectronics architectures such as foundry access. This talk discusses recent advances in photonic neuromorphic networks and provides a vision for photonic information processors. Details include, 1) a comparison of compute performance technologies with respect to compute efficiency (i.e. MAC/J) and compute speed (i.e. MAC/s), 2) a discussion of photonic neurons, i.e. perceptrons, 3) architectural network implementations, 4) a broadcast-and-weight protocol, 5) nonlinear activation functions provided via electro-optic modulation, and 6) experimental demonstrations of early-stage prototypes. The talk will open up answering why neural networks are of interest, and concludes with an application regime of PNN processors which reside in deep-learning, nonlinear optimization, and real-time processing. Photonic neural networks (PNN) are a promising alternative to electronic GPUs to perform machine-learning tasks. The PNNs value proposition originates from i) near-zero energy consumption for vector matrix multiplication once trained, ii) 10-100 ps short interconnect delays, iii) weak required optical nonlinearity to be provided via fJ/bit efficient emerging electrooptic devices. Furthermore, photonic integrated circuits (PIC) offer high data bandwidth at low latency, with competitive footprints and synergies to microelectronics architectures such as foundry access. This talk discusses recent advances in photonic neuromorphic networks and provides a vision for photonic information processors. Details include, 1) a comparison of compute performance technologies with respect to compute efficiency (i.e. MAC/J) and compute speed (i.e. MAC/s), 2) a discussion of photonic neurons, i.e. perceptrons, 3) architectural network implementations, 4) a broadcast-and-weight protocol, 5) nonlinear activation functions provided via electro-optic modulation, and 6) experimental demonstrations of early-stage prototypes. The talk will open up answering why neural networks are of interest, and concludes with an application regime of PNN processors which reside in deep-learning, nonlinear optimization, and real-time processing.

The traditional ways of tuning a Silicon photonic network are mainly based on the thermal-optic effect or the free carrier effect of silicon. The drawbacks of these methods are the volatile nature and the extremely small change in the complex refractive index (Δn<0.01). In order to achieve low energy consumption and smaller footprint for applications such as photonic memories or computing, it is essential that the two optical states of the system exhibit high optical contrast and remain non-volatile. Phase change materials such as GST provide a solution in that it exhibits drastic contrast in refractive index between the two non-volatile crystallographic states which can be switched reversibly. Here, we first show that GST can be integrated with a Si ring resonator to demonstrate a quasi-continuous optical switch with extinction ratio as high as 33dB. Secondly, we demonstrated GST-integrated 1×2 and 2×2 Si photonic switches using a three-waveguide coupler design which exhibits a low insertion loss of ~1dB and a compact coupling length of ~30μm. The crosstalk is as small as -10dB over a bandwidth of 30nm.

We present the design of tunable infrared absorbers/emitters based on hybrid metal / vanadium dioxide microstructures. We demonstrate tuning and extinction of infrared absorption peaks, based on the phase transition of vanadium dioxide from insulator to metal states. We assess the performance of specific optimized designs as thermal rectifiers, capable of allowing heat flow in one direction only. We optimize the structural parameters to maximize the rectification ratio. We then further adjust the material loss of the vanadium dioxide to determine the ideal loss values for this application. Intuitively, the results suggest that the loss in the metallic state should closely resemble that of the other metal used in the microstructure. The results thus suggest future directions for materials development efforts.

The development of low-loss optical phase change materials (O-PCMs) promises to enable a plethora of nonvolatile integrated photonic applications. However, the relatively large optical constants change between different states of calls for a set of new design rationales. Here we report a non-perturbative design that enables low-loss device operation beyond the traditional figure-of-merit limit. The basic design rationale is to engineer the light propagation path through the OPCMs when it is in the low-loss amorphous state, and divert light away from the lossy crystalline state leveraging the large mode modification induced by the O-PCM phase transition. Following this approach, we demonstrate broadband photonic switches with significantly enhanced performances compared to current state-of-the-art.

Two-dimensional, atomically-thin, materials have received enormous interest as a result of their unique mechanical, electrical and optical properties. Particularly exciting are the transition metal dichalcogenides – atomically-thin semiconductors that possess an electronic band gap in the visible. Although these materials have been investigated for applications in opto-electronics, not much work has focused on these systems as a platform for quantum photonics and quantum optics. In this talk I will describe two approaches that leverage atomically thin semiconductors, and other two-dimensional materials, assembled in layered van der Waals heterostructures for applications in these areas. In the first part of the talk I will describe the unique photophysical properties of quantum emitters hosted by single layer transition metal dichalcogenides. I will describe our recent efforts to control the confined excitons via the application of electric fields and strain. Finally, I will report on the observation of the coherent evolution of quantum emitters in the insulator hexagonal boron nitride.

Publisher’s Note: This conference presentation, originally published on 9 September 2019 was withdrawn on 29 October 2019 per author request.

Historically, strong light-matter interaction is achieved by using either high quality factor (Q) micro-resonators such as photonic crystal cavities which enable long photon lifetimes, or metallic nanoresonators which allow for strong field enhancements provided by localized plasmon resonances. However, it has been recently demonstrated that a hybrid system, which combines both a dielectric cavity and a dipolar plasmonic antenna, can achieve stronger emission enhancements than the cavity or antenna alone [ACS Photonics, 3 (10) (2016)]. We propose to use arrays of N plasmonic antennas to further engineer the directionality of this enhanced emission. We analyze the resonant mode structure and local density of states in high-Q hybrid plasmonic-photonic resonators composed of a dielectric disk, perturbed by dimers of plasmon antennas, systematically swept in position through the cavity mode. A simple cavity-perturbation-theory model shows how the degenerate clockwise and anticlockwise whispering gallery modes (WGMs) of the unperturbed cavity split into two new hybrid modes with different complex eigenfrequencies, showing an interesting evolution of the resonance frequencies and Q's as the antenna spacing is varied. We find that one may construct large LDOS enhancements exceeding those given by a single antenna, which are `chiral' in the sense of correlating with unidirectional injection into the cavity. We report an experiment probing the resonances of silicon nitride (Si3N4) microdisks decorated with Aluminium antenna dimers that confirms the predicted mode properties as function of antenna spacing.

Embedding Ge-quantum dot emitters in Mie resonators leads to an enhancement of their luminescence efficiency due to the Purcell effect. To increase this effect, collective Mie resonances in extended Mie-resonator chains are investigated leading to a partial cancellation of radiation losses and experimentally observed Q-factors of up to 500. The corresponding modes and their field localization are theoretically analysed and traced back to a combination of individual oscillating dipoles.

We will demonstrate that the incorporation of active media with extremely small gain coefficients inside epsilon-near-zero (ENZ) plasmonic waveguides will cause the formation of exceptional points and spectral singularities (light amplification). Note that the realization of these points with symmetric reciprocal plasmonic configurations is still elusive mainly due to the weak light-matter interaction at the nanoscale. These intriguing effects will lead to several novel functionalities, such as reflectionless ENZ response, slow light, and nanolasing. Moreover, we will demonstrate that the entanglement of two or multiple emitters placed inside the ENZ nanochannels, even without incorporating gain (lossy ENZ case), will be enhanced over extended areas, which are comparable or even longer than the wavelength of the emitted radiation. Our findings can be applied to improve the response of optical quantum computers, such as the efficient control of long distance entanglement between qubits.

Scaling up the radiance of coupled laser arrays has been a long-standing challenge in photonics. In this study, we demonstrate that notions from supersymmetry—a theoretical framework developed in high-energy physics—can be strategically used in optics to address this problem. In this regard, a supersymmetric laser array is realized that is capable of emitting exclusively in its fundamental transverse mode in a stable manner. Our results not only pave the way toward devising new schemes for scaling up radiance in integrated lasers, but also, on a more fundamental level, could shed light on the intriguing synergy between non-Hermiticity and supersymmetry.

High-refractive index dielectric nanostructures with both electric and magnetic responses to external optical field have recently become a hot topic in nanophotonics. The resonances inside these particles at subwavelength scale are governed by the nanoparticle geometry and can be described by Mie theory. There has been many potential applications based on this concept such as: light beam focusing, bending, hologram generation, etc. Recently, lasing behavior have been realized in these systems by combining these resonance with the bound state in the continuum. In this presentation, we will show how to engineer these resonances and their strong coupling effect to create effective optical cavities for lasing with controlled emission directionality both in-plane and out-of-plane. The coupling of Mie resonances will be discussed in three different cases: 2D arrays, 1D chains and single nanoparticles. In all cases, by carefully designing the geometry and periodicity of these nanoparticles, highly localized states or so-called supercavities can be formed by strong coupling of dipole or multipole resonances of individual nanoparticles. Using GaAs – a common III-V semiconductor- as both dielectric nanoantenna and gain medium, we demonstrate experimentally unprecedented lasing behavior in these systems by optical pumping at cryogenic temperature. Our design concept will provide a guideline for nanolasers with controllable directionality for optoelectronic applications.

Detection of faint fluxes of photons at terahertz frequencies is crucial for various applications including biosensing, medical diagnosis, chemical detection, atmospheric studies, space explorations, high-data-rate communication, and security screening. Heterodyne terahertz spectrometers based on cryogenically cooled superconducting mixers have so far been the only instruments that can provide high spectral resolution and near-quantum-limited sensitivity levels. The operation temperature, bandwidth constraints, and complexity of these terahertz spectrometers have restricted their use to mostly astronomy and atmospheric studies, limiting the overall impact and wide-spread use of terahertz technologies. Here we introduce a spectrometry scheme that uses plasmonic photomixing for frequency downconversion to offer quantum-level sensitivities at room temperature for the first time. Frequency downconversion is achieved by mixing terahertz radiation and a heterodyning optical beam with a terahertz beat frequency in a plasmonics-enhanced semiconductor active region. We demonstrate spectrometer sensitivities down to 3 times the quantum-limit at room temperature. Our presented spectrometry scheme can be applicable to resolve both the high-resolution spectra of gas molecules and mid-resolution spectra of condensed phase samples over a total operable bandwidth of 0.1-5 THz. As an example, we use the presented spectrometer to resolve the spectral information of ammonia, which has a number of narrowband absorption peaks over the 0.1-5 THz frequency range. With a versatile design capable of broadband spectrometry, this plasmonic photomixer has broad applicability to quantum optics, chemical sensing, biological studies, medical diagnosis, high data-rate communication, as well as astronomy and atmospheric studies.

We present a comprehensive investigation of resonant all-dielectric multi-layers. We first introduce a numerical as well as analytical optimization based on admittance recurrence law. We then address the technological aspects of the fabrication using dual-ion-beam sputter deposition. Using the optimally fabricated structures, we carry out experiments to optically characterize their responses in the near and far fields. Previously, our optimization strategy had been based on maximizing the absorption within the dielectric stack [1] for any illumination conditions without altering the field enhancement. Recently, we have improved this process by introducing a single zero-admittance layer that allows defining the field enhancement localization within the multi-layer [2]. Similarly to the Kretschmann configuration for surface plasmon resonances (SPR), these resonant all-dielectric components work under total internal reflection but they can support field enhancements up to 104-105. From a theoretical point of view, the enhancement is not intrinsically limited (except for nonlinear phenomena or material damages under high flux), and it is therefore the illumination bandwidths (angular divergence and spectral range), which mainly limit the resulting field enhancement [3]. We will introduce the resonant all-dielectric components, demonstrate their potential for sensing applications and give a brief comparison with SPR [4]. The authors acknowledge the PSA group for financial support of this work, the ANRT for their support through the CIFRE program and the RCMO Group of the Institut Fresnel for the realization of the coatings. This work is part of the OpenLab PSA/AMU: Automotive Motion Lab through the StelLab network. 1- Appl. Phys. Lett. 103, 131102 (2013) 2- Phys. Rev. A 97, 023819 (2018) 3- Opt. Express 25, 14883 (2017) 4- Appl. Phys. Lett. 111, 011107 (2017)

In near-field TPV cells, the effects of the necessary front electrode are considered and shown to be of great importance. The electrode tradeoff between required high dc conductivity but low photonic absorption becomes detrimental for the efficiency in the very near field, as the thermal-emitter evanescent waves decay fast and are absorbed inside the electrode without penetrating sufficiently into the semiconductor. Therefore, near-field cells fail to deliver ultra-high power efficiently, as hoped. Still, efficient mid-power conversion is possible, and we compare the performance of several tunable-by-doping conducting-electrode materials. Moreover, novel phenomena arise in the near field, such as the inability to use thick transparent electrodes, while instead the feasibility of ultra-thin ‘opaque’ ones. The metallic-grid fingers exhibit an ‘anomalous’ shading loss, significantly smaller than predicted by geometry, by suppressing the thermal emission in the emitter regions across them.

The promise of high-resolution imaging beyond the diffraction limit has been a core motivation for research in the fields of metamaterials and plasmonics. However, the problems with material losses have quelled some of the enthusiasm which once existed. Here, we review our recent approach relying on imaging theory and correlations to push the limits of super-resolution imaging in the presence of losses and noise. Starting with plasmon injection scheme for compensating losses, we subsequently extended the same principle to a broad range of near-field and far-field imaging systems involving both coherent and incoherent light, and hence termed this approach more encompassing active convolved illumination" (ACI). In ACI a relatively narrow range of spatial frequencies are amplified at a time. Since the total power in the active image does not change significantly, the spectral SNR is significantly improved in the region of amplification. This improves the overall resolution of the images. We also present potential extension of ACI into different research domains including atmospheric imaging, time-domain spectroscopy, and quantum computing.

Nonlinear optical processes provide completely new contrast mechanisms for microscopy. The polarization vector of a focused field is three-dimensional (3D) and spatially inhomogeneous, thereby opening up new opportunities for the characterization of complex nano-objects. The 3D control of focal fields further benefits from the use of unconventional states of polarization, e.g., radially (RP) and azimuthally polarized (AP) incident beams. Of particular importance is the fact that focused RP beam gives rise to a strong longitudinal electric-field component at the focus. In contrast, focused AP beam maintains a strictly transverse electric-field distribution in the focal volume, mimicking the structure of the incident beam before focusing. In this Paper, we summarize several new capabilities and additional benefits made possible by vector beams in nonlinear microscopy of various types of nano-objects. As one of the first demonstrations, we have shown that second-harmonic generation microscopy with vector beams has superior sensitivity to the morphology of individual metal nanoparticles. We have also shown that efficient coupling of incident light to metal nano-objects requires tailored focal fields matching the modes of individual particles and even their assemblies (or so-called oligomers). We also used vector beams to characterize the crystal structure of semiconductor nanodisks and to couple light to vertically-aligned semiconductor nanowires. In addition, nanowires have been used to probe the longitudinal fields of advanced polarization states in three dimensions.

Localized surface plasmon resonances can increase the quantum efficiency of photon emitters through both absorption and spontaneous emission enhancement effects. Despite extensive studies, experimental results that clearly distinguish the two plasmonic enhancement effects are rarely available. Here, we present clear spectral signatures of the plasmonic enhancement effects on the absorption (excitation) and spontaneous emission (Purcell factor) by analyzing the temperature dependent photoluminescence (PL) properties of InGaAs/GaAs single quantum well (QW) coupled to colloidal gold nanorods (AuNRs) at different GaAs capping layer thickness (d). We find that when the emitting InGaAs layer is close to the AuNRs (d = 5 nm), the plasmonic enhancement effect on the QW PL is dominated by the Purcell factor that significantly increases the external quantum efficiency of the QW that otherwise barely emits. When d is increased to 10 nm, the temperature dependence of the PL enhancement factor (F) reflects absorption enhancement in the capping layer followed by carrier diffusion and capture by the well. First F increases with temperature and then decreases following the temperature dependence of the carrier diffusion coefficient in GaAs. By factoring out the contribution of the captured carriers to F, it is shown that carrier transfer to the well reaches saturation with increasing incident laser power. In addition to providing insight into the plasmonic enhancement mechanism, the results presented in this work suggest that colloidal plasmonic nanoparticles can be used as simple probes for understanding carrier transport phenomena in arbitrary semiconductor heterostructures.

In this work, we experimentally study the carrier and refractive index dynamics of InGaAs nanopillar grown on a Si on insulator (SOI) substrate. The recombination process of the InGaAs NP is characterized with different optical techniques. Temperature dependent photoluminescence (PL) at 0.5mW excitation power is carried out to determine the influence of temperature on carrier dynamics. The radiative recombination lifetime has been studied at 7K from time-resolved photoluminescence (TRPL) experiments at a certain excitation power. The optimal combination of pitch (separation between NPs) and diameter in the growth process of this nanostructure has also been measured. These results will contribute to further optimization of the InGaAs nanolaser for integration of III-V optoelectronics on SOI substrates.

The ability to probe and control light-matter interaction at the nanometer scale not only advances frontiers of fundamental science, but also is a critical prerequisite to device applications in electronics, sensing, catalysis, energy harvesting, and more. Exploiting and enhancing the originally weak light-matter interactions via nanofabricated photonic structures; we will be able to sense chemical species at single molecule levels, to devise better imaging and manufacturing tools, to transfer data more efficiently at higher speed. In this invited talk, I will present recent progress in Prof. Xiang Zhang's group on the subject of light-matter interaction in perovskites.

Pulsed dynamics are rigorously studied in coupled silicon photonic crystal cavity-waveguide nanostructures by developing a computational model based on coupled-mode theory, which describes cavity-waveguide coupling effects, key nonlinear interactions, such as the Kerr effect, two-photon-absorption, free-carrier (FC) dispersion and FC absorption, as well as waveguide dispersion effects. Propagation of optical pulses in a photonic system consisting of two photonic crystal cavities coupled to a photonic crystal waveguide operating in the slow-light regime is analyzed. Moreover, the influence of different parameters on pulse dynamics is investigated, including the separation between cavities, the distance between the cavities and the waveguide, and the input pulse width.

We model a photonic crystal slab as a Fabry-Perot resonator with two propagating Bloch waves in the periodic medium. This provides a semi-analytical recipe for the computation of photonic crystal slab modes' dispersion and quality factors. We apply for the search and study of bound states in the continuum, which exist above the light line, among the leaky modes, but nevertheless are decoupled from the continuum of propagating modes and are confined inside the periodic medium. We identify them as a set of optogeometric parameters for which the quality factor of a given photonic crystal mode goes to infinity. Also, we illustrate a simple example of the vertical symmetry breaking by adding a semi-infinite dielectric substrate, and comment on some other asymmetric configurations.

In this study the effect of the concentration of acrylamide and the influence of different initiators in a photopolymer composition for holographic recording of diffraction gratings is investigated. Light manipulating Holographic Optical Elements (HOEs) have a number of characteristics which can be optimised for different roles. However, at the core of these devices is the refractive index modulation that has been created in the material during recording. Typically higher refractive index modulation will enable greater diffraction efficiency. Solar concentrating HOEs can particularly benefit from material that experiences higher refractive index modulation. For a solar concentrator to have a high acceptance angle thinner photopolymer layers are preferable. Thinner layers can lead to a reduction of the device’s diffraction efficiency unless the refractive index modulation increases to compensate.

This paper presents an optimisation of a photopolymer formulation for improved refractive index modulation and sensitivity of the layer. An increase in the acrylamide concentration of 66% resulted in 50% higher refractive index modulation with values reaching 5 × 10⁻³ in 40 micron layers.

Faster recording times are an important consideration for the commercialization and mass production of photopolymer devices [1]. Higher production rates and lower costs are some of the main advantages. Altering the initiator is expected to have an effect on the material’s sensitivity and thus on recording time.

Several initiators were compared, triethanolamine (TEA), methyldiethanolamine (MDEA) and dimethylethanolamine (DMEA). It was found that holograms recorded with MDEA as the initiator recorded 58% faster over TEA based photopolymer at larger layer thicknesses.

The stability of the photopolymer was also tested with different protective coatings when subjected to UV light. The properties exhibited by this photopolymer composition make it a promising candidate for development of solar concentrating applications; however improvements to the durability in conditions of UV radiation will have to be made before it is suitable for solar concentration.

Photopolymer nanocomposite materials utilising nanoparticles of varied refractive index are one of the most attractive materials for holography due to their tuneable properties. The preparation of the photopolymer nanocomposites can involve mixing a stable colloidal suspension in the photopolymer solution or printing of the nanoparticle colloidal suspension on top of a dried photopolymer layer. By following the first approach in this study a novel photopolymer nanocomposite material is prepared for holographic recording. It consists of N-isopropylacrylamide (NIPA)-based photopolymer as a host and iron oxide magnetic nanoparticles as nanodopant. The methodology of the photopolymer nanocomposite material preparation is explained in detail. In order to investigate the interaction of nanodopants with the host photopolymer, the photo-bleaching of the layers when exposed to a single laser beam has been studied. Initial characterisation of the holographic recording capability of the nanocomposite has been carried out. The maximum diffraction efficiency (DE) achieved in 70 μm thick layer after recording with 3.4 mW/cm² intensity at 532 nm wavelength is 18 %.

Dynamic control of light by surface plasmon resonance is applicable for mechanically tunable photonic devices, such as variable color filters, tunable Neutral Density (ND) filters, and adjustable surface-enhanced Raman scattering (SERS) substrates. We experimentally demonstrated dynamic tuning of plasmon resonance using the strain-controlled elastic device of close-packed gold nanoparticle array that was fabricated by self-organized technique. By applying the uniaxial strain, the plasmon peak wavelength blue-shift of 23 nm under parallel polarization to the strain direction and red-shift of 27 nm under perpendicular polarization, and the total tunable range was achieved to 50 nm. In addition, by applying the biaxial strain, peak shifts in the strain are monotonic for both linear polarizations, which is clear advantages for practical optical applications.

We present an optomechanical impact sensor, designed by the utilization of a 2D rod-type photonic crystal (PhC) cavity. The PhC cavity is sandwiched by perfect electrical conductor (PEC) boundaries with an air slot between the top of the PhC rods and the bottom of the top PEC layer. Strong light localization in the air slot region makes the PhC cavity characteristics highly sensitive to the air slot width, leading to optomechanical applications such as impact sensing. A suspended mechanical gold membrane, as a replacement of PEC layers for practical realizations, is designed to sense impact acceleration. In the presence of an impact, the mechanical structure deflects resulting in a change in the air slot height, which in turn, tunes the resonant wavelength of the PhC cavity. Calculations show that 16.6 μs response time, much faster than the commercially available ones (around 200 ms), is possible.

In this work we address the issue of nonlinear modes in a two dimensional waveguide array, spatially distributed in the Lieb lattice geometry, modeled by the discrete nonlinear Schrodinger equation. In particular, we analyzed the existence and stability of vortex-type solutions in this system and we found two main kind of vortex modes, namely the on-site and off-site, ranging from S = 1 to S = 3. We study their stability in function of coupling anisotropy effect, finding different behaviours according to the topological charge of solutions.

While several approaches have been proposed to optimize the geometrical dimensions of multilayer photonic nanostructures with a given material composition, very few works have considered simultaneously optimizing the material composition and dimensions of such nanostructures. Here, we develop a hybrid optimization algorithm as a method to design optimal multilayer photonic structures. Leveraging recent progress in metaheuristic optimization, we develop an optimization method consisting of a Monte Carlo simulation, a continuous adaptive genetic algorithm, and a pattern search algorithm. We first perform a Monte Carlo simulation over the entire design space. Structures are ranked according to the chosen fitness function. We find that this method yields viable material compositions. The material compositions of the best structures are used to parameterize the genetic algorithm in the next stage. A number of genetic algorithm populations are generated, one for each material composition, to optimize the thicknesses. These populations are run in parallel for a number of generations, evaluating the structures of each generation and using the characteristics of those that best satisfy the fitness function to improve other structures. The resulting populations converge towards the optimum of their solution space typically after a few thousand generations. The genetic algorithm used is continuous because parameters are treated as real numbers rather than bit strings as in classical genetic algorithms, and adaptive because the algorithm uses characteristics of the population pool to guide optimization. Finally, we apply a pattern search local optimization algorithm to the best result from each population to find the exact optimum.